I'm starting too

I'm starting to get some rust on the bottom of my passenger door. Is there an easy way I can fix this?

I would sand or sandblast the rust, coat it with a rust preventative product like Zero Rust or POR-15. You need to stop it from oxidizing any further.
Take off the door panel and treat the inside too, especially on the bottom along the seam.
Zero Rust can be used a primer and can be "Bonbo-d"/painted over.
If you have rust on your doors you may want to look under your carpet too.
Good luck.